Many cities have for a long time disposed of garbage by burying it in surrounding areas which are often of low grade level. Hence, such garbage disposal also serves as land fill. The buried garbage decomposes and generates gas containing methane and carbon dioxide as the principal components. Such garbage gas, euphemistically called land-fill gas, has attracted attention as a potential fuel gas in view of its methane content, generally in the range of about 50 to 70% by volume. Carbon dioxide being the other principal component of land-fill gas, generally in the range of about 25 to 45% by volume, must be materially eliminated before the land-fill gas can be utilized in existing fuel gas distribution systems.
The removal of carbon dioxide from gas mixtures is an extensive art. Known processes for the separation of carbon dioxide from other gases utilize refrigeration to cause solid carbon dioxide deposition, a molecular sieve to capture carbon dioxide, chemical absorption, or a system combining such techniques. Scrubbing a gas with methanol to remove carbon dioxide has been incorporated in several different processes which require considerable equipment and, hence, a high capital expenditure.
Methane-containing gases with a high content of carbon dioxide, such as land-fill gases, have not heretofore been seriously considered for fuel purposes because of the high cost of separating carbon dioxide therefrom by known methods.
Accordingly, a principal object of this invention is to provide a process for economically removing a major portion of the carbon dioxide present in gases in which methane is the principal component.
Another object is to provide a simplified plant for eliminating the bulk of the carbon dioxide in gases having a predominant content of methane.
A further object is to treat methane-containing gases having an appreciable content of carbon dioxide to yield fuel gases of high heating value.
These and other objects and advantages of the invention will be evident from the description which follows.